'Soundscape ecology': the new science helping identify ecosystems at risk

As industrial development and human encroachment intensifies globally, academics believe the study of natural soundscapes could teach us much about how ecosystems function - and how they are under threat

‘Acoustics tie us to nature. Natural, ambient sounds give us a picture over time and define place. Sound also carries information about the time of day or seasonal time; every landscape has a rhythm to it. Cicadas here in the Midwest are very loud in the late summer – in fact they’re called Dog Days cicadas. As humans we’ve become accustomed to what these natural sounds are but as ecologists we haven’t studied their meaning in a very holistic way....' Dr Bryan C. Pijanowski and his colleagues at Purdue University, Indiana seek to change that by pioneering the emerging science of soundscape ecology.

To get an overview of a soundscape it's necessary to study the biophony (sounds that come from animals), geophony (geophysical signals that are the result of the movement of wind and water and earth) and anthrophony (sounds produced by human activity). As Dr Pijanowski explains: ‘The idea is to study the patterns of all of these, how they occur and emerge in different landscapes around the world. From this we can learn about ecosystems and how they function, and how these ecosystems might be threatened by the measure of anthrophony, because anthrophony provides us with a reflection of the amount of human activity that occurs in a landscape.’

By its nature soundscape ecology is interdisciplinary and collaborative. ‘It’s based on a lot of work that’s been done by bioacoustics experts – who have been studying birdsong and vocalisation and communication in animals for decades. We’re also building upon the work of acoustic ecologists who have turned their ears to natural sounds and who are often musicians. They have provided us with a rich vocabulary to begin to think about these natural soundscapes. Then there are cognitive psychologists who know how vertebrates process acoustic information and how certain kinds of sounds can give us an emotional response.’

The team at Purdue are trying to bring all this together: ‘We’re saying for the first time that that soundscape is fully a reflection of the landscape.’ Implicit in this is that soundscapes should be treated as equally important and preserved with as much zeal as the landscapes we can see. Previously no-one had thought about developing a system of classification for soundscapes but this new field aims to do just that while also thinking about how we might start working to protect them.

‘We’re interested in identifying soundscapes that might be threatened and that if lost would mean losing part of the acoustic heritage of the earth. There are some that are phenomenal and unique and are only found in one location.’ Human activity and the anthrophonic sounds arising from it are one of the main drivers of change in soundscapes, while climate change is another. Can the study of sounds be used to discover if something is wrong in an ecosystem?

Understanding climate change

‘Because geophony is a reflection of climate we think we’ll be able to use it as a means to understand climate change. A lot of the organisms that vocalise are temperature-dependent like insects and amphibians. So climate change could alter the natural soundscapes in ways that might be important to ecosystems – affecting things such as predator-prey relationships.’

A good deal of research has been done at La Selva biological station in Costa Rica. In that environment, streams are very noisy after rainfall and this explosion of geophony occupies a lot of the acoustic space. ‘For organisms that are trying to vocalise and find mates, if the climate was to change and it stayed rainy for longer or shorter periods it could seriously affect their chances of reproducing, because the geophony is so dominant in that landscape and when the rains stop everyone is vocalising.'

Climate change can alter geophony and there could be a compression of vocalisation opportunities in time. Sonic diversity can also be a sign of a healthy ecosystem. A study published by Pijanowski and colleagues in March 2011 in the journal Bioscience suggested that in undisturbed forest the acoustic niches are very complex, with a lot of biological signals present. But as you move into more human-dominated landscapes far fewer biophony patterns are found. The dawn chorus and dusk chorus dwindle or don’t exist at all in many human-dominated landscapes.

‘There have been several papers published in high-profile journals like Nature and Science in the last few years where we’re beginning to see these interactions between anthrophony and biophony’, says Pijanowksi. ‘There are a lot of different kinds of biological responses to noise in landscapes. For example, birds can begin to sing louder, or raise the pitch of their singing, to make their voices heard across the noisy landscape. Or in some cases they may shift to singing at night, when it’s quieter.’

Landscape ecology

‘Some organisms are more adaptable and so can alter their behaviour to deal with a noisy environment, but others like insects stridulating that are fixed in their frequency patterns and so if they’re drowned out they’re just drowned out for good. Nesting success can be affected as well. We’ve just published a series of papers in Landscape Ecology that looked at soundscape ecology in a variety of perspectives and some of these showed that bird behaviour really suffers in noisy environments.’

An important distinction is that anthrophony tends to be just noise with no meaning, whereas natural soundscapes are communicative networks buzzing with information. The Purdue University soundscape ecology research project is trying to use information theory to extract these complex biophonic signals from the background hum of anthrophony.

‘One of the things we’ve been doing here in Indiana is setting up acoustic sensors in all different kinds of habitats. We’ve been recording continuously, day and night, for about four years. We now have a tremendous amount of data and we’re beginning to analyse how different habitats vary in their acoustic signals.’

Soundscapes exist everywhere and the need to safeguard our natural acoustic heritage is surely something which should be emphasised more. But urban environments are places where we can exercise positive design to create the soundscape or change it for the better. Dr John Levack Drever, a composer and acoustic ecologist at Goldsmiths, University of London, explains that a lot of contemporary thinking in this area goes back to the great listener Murray Schafer.

‘Schafer says that the reason cities are getting louder is that we don’t know how to listen, and nobody is properly trained to design sounds. In order to design environmental sound to better ends we first need to learn to resensitize our listening and to then design from that perspective.’

Noise mapping

The particularities of place are central to this, the meaning and memories of sound, and all the sonic associations we carry with us. ‘Schafer shifted emphasis away from just the noise aspect, which had been the main focus when thinking about soundscapes up until that point, to considering more positive soundscape design.’

Dr Drever complains that acousticians aren’t expected to make qualitative judgements about sound, but rather just measure ‘sound pressure levels’ (volume). These data are fed into Defra’s Noise Mapping department that seeks to work out where ‘noise hotspots’ are and formulate action plans to tackle them. ‘But the whole thing of course is a huge generalisation and a huge oversimplification; it doesn’t involve people and their perceptions or a dialogue about how we want our cities and environments to sound.’

‘There has to be a closer dialogue between a community of creative listeners like musicians and sound artists (who are working with environmental sound and its qualitative aspects) and the engineers and architects who craft our soundscapes. We also need to evaluate the sounds that might already be here before a major rebuild takes place. I am also wary of how soundscape design can be used as a marketing tool, and the sterile corporate soundscape that we might be moving towards.’

There is also serious concern about sounds that are beyond the hearing range of the average adult. Dr Drever adds: ‘We might not be completely aware of how frequencies we can’t hear (for example those below 20 Hz) might be affecting us, especially when they’re at very high levels. At the other end of the spectrum, frequencies of 16 kHz and higher are used to keep “undesirable” teenagers away from certain places. Even if you’re broadcasting frequencies that the average adult can’t hear, you’re still filling the space with frequencies, potentially at quite high volumes. The main worry is always that somebody is going to have permanent hearing damage. But these volumes and sounds can affect you in other ways... And what about species that use that range of frequencies?’

Both Pijanowski and Drever advocate and practice soundwalking in order to reconnect with the soundscapes in which we dwell. Dr Drever reveals that he has ‘always been amazed at the level of listening that’s happened. People really have quite profound experiences when all they’re doing is listening.’

In future will we perhaps see the emergence of an ecotourism of the ear?

In the meantime there is an enormous amount of concerted listening, recording and analysing to be done in order to conserve soundscapes that are crucial to our natural and cultural heritage. Dr Pijanowski: ‘It’s my hope that our research could impact on policy that regulates noise and helps protect the natural soundscape. We’re in danger of severing our acoustic link with nature. We often seem to no longer hear it or see it – and does that mean we no longer value it, as a species?’

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